Magnetic digital ammeter

ABSTRACT

IN A MAGNETIC DIGITAL AMMETER UNKNOWN ANALOG CURRENTS ARE COMPARED WITH KNOWN DIGITAL INPUTS IN A SINGLE CORE FOR COMPARISON PURPOSES. THE CORE HAS A MAGNETIC CHARACTERISTIC OF A HIGH PERMEABILITY AT THE ORIGIN WITH A VERY SMALL CROSS-SECTION WHEREBY SMALL MAGNETO MOTIVE FORCES WILL SATUREATE THE CORE MATERIAL. THE COMPARISON OF THE ANALOG SIGNALS TO THE DIGITAL SIGNALS IS ACCOMPLISHED BY CAUSING BOTH MAGNETO MOTIVE FOCES PRODUCED BY THE TWO SIGNALS TO GO TOWARD ZERO AND NOTING THE POLARITY OF THE BACK ELECTRO MOTIVE FORCE DEVELOPED. THE SERIES OF BACK E.M.F. OR &#34;KIK&#34; POLARITIES IS EMPLOYED TO ALTER THE DIGITAL MMF SO THAT IT APPROACHES THE SIGNAL MMF IN MAGNITUDE. THE VERY SMALL CROSS-SECTION OF THE CORE PERMITS RAPID SWITCHING SINCE A LARGE NET MMF DECREASES TOWARDS A MINIMAL NET MMF WITH LITTLE DELAY OWING TO THE NEED FOR A LARGE CHANGE OF FLUX.

P. E. SLAVIN MAGNETIC DIGITAL AMMETER Feb. 16, 1971 Filed Jan. 5, 1967FIG. I

I N VEN TOR.

TER E SLAVIN TIME United States Patent US. Cl. 340347 3 Claims ABSTRACTOF THE DISCLOSURE In a magnetic digital ammeter unknown analog currentsare compared with known digital inputs in a single core for comparisonpurposes. The core has a magnetic characteristic of a high permeabilityat the origin with a very small cross-section whereby small magnetomotive forces will saturate the core material. The comparison of theanalog signals to the digital signals is accomplished by causing bothmagneto motive forces produced by the two signals to go toward zero andnoting the polarity of the back electro motive force developed. Theseries of back E.M.F. or kik polarities is employed to alter the digitalMMF so that it approaches the signal MMF in magnitude. The very smallcross-section of the core permits rapid switching since a large net MMFdecreases towards a minimal net MMF with little delay owing to the needfor a large change of flux.

BACKGROUND OF THE INVENTION (1 Field of the invention This invention isdirected generally towards improvements in code converters and moreparticularly is directed towards a new and improved system forconverting unknown electrical currents into known digital data. Thesystem may be defined as a magnetic digital ammeter.

(2) Description of the prior art In my US. Pat. No. 3,231,886 dated Ian.25, 1966, there is disclosed a system for converting an analog currentto decimal digits. The system described and illustrated therein includesa magnetic core in which signal magnetizing forces opposed digitalmagnetizing forces. The polarity of the net magnetizing force in thecore is sensed by causing both analog and digital signals to go to zeroto produce a back or kik. The polarity of the backpulse was used toalter the digital MMF so that it approached the signal MMF. Within ashort time, the two opposing MMFs were closely equal and the digitalMMFs switches could be read out as a number. In this manner the analogsignal is converted into a digital display. The present inventionconcerns itself with improvements on the above converter andspecifically relates to a novel core circuit arrangement for improvingthe speed, stability, economy, precision and resolution of a magneticdigital ammeter. Speed is increased by reducing the time required toarrive at equality between the analog and digital signals, this timebeing the period required to produce the magnetic flux change. Thepresent system is adapted to detect small net MMFs Without causing thesignal current in the converter to go to zero. This invention featuresmeans for changing the digital MMF by a change of winding turns only,thus giving an increase in stability and an economy in the use ofprecision resistors employed in the circuit. The invention also featuresmeans to minimize the effect of the kik polarity of very small mismatchof times on switching the MMFs toward zero.

3,564,534 Patented Feb. 16, 1971 The invention features a magneticdigital ammeter comprising a core of very small cross-section and havinga magnetic characteristic of a high permeability slope at the origin.The core is provided with three sets of windings, one set for applyingunknown analog signals to the core, another set for applying knowndigital signals to the core in a direction opposing the analog signalsand a third set for detecting the polarity of the net MMF. The digitalwindings are connected to a precision resistor and switching means,responsive to the detected polarity in the core, are provided forcausing a change in the number of digital turns whereby a singleprecision current through a single precision resistor may be em ployedto give a plurality of different MMFs corresponding to a decimal digit,all of these MMFs being stable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a curve showing the magneticcharacteristics of a transformer in the form of an annular core employedin the invention,

FIG. 2 is a somewhat schematic diagram of the windings on thetransformer core and their associated circuitry, and

FIG. 3 is a timing diagram illustrating the sequence of opening andclosing of the several switches in the circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of thedrawings, there is shown the magnetic characteristic curves of twodifferent annular transformer cores for use in comparing known digitalMMFs to unknown analog signal MMFs. The broken line curve 4 is for acore of the type employed in my US. Pat. 3,231,886 and the solid linecurve 5 is for a core used in the present invention. In the curves ofFIG. 1 the horizontal axis 2 represents MM-F (mag netic force) and thevertical axis 1 represents magnetic flux (field strength). A vector 8represents a signal MMF which is almost equal to an opposing digital MMFindicated by a vector 7 so that a net MMF appears as a small vectorindicated by reference character 9. The polarity of the vector 9 isdetected by causing both MMFs, indicated by vector lines 7 and 8respectively, to go toward zero. This will cause a flux change in thenegative or down direction of that small part of the magneticcharacteristic curve 3.

At the start of the balancing process the digital MMF' is reset to zero.It is then evident that the net MMF will be a large vector to the rightas viewed in FIG. 1. As this net MMF becomes smaller, the flux will haveto change down along the curve 4. A large ,flux change corresponding tothe high slope of the curve 4 means that a large volts-time product isrequired to force this flux. That is to say it will take a relativelylong time to approach a balanced condition within the core.

A high initial permeability (slope) can be achieved and yet limit theabove flux change if the material be such as sold under the trademarkSupermalloy but having a cross-section which will be minimal, typicallyon the order of a few wraps of 4; mil tape for a saturation flux changeof about 5.0 maxwells. This characteristic is represented by the curve 5and 5' in FIG. 1 and yields a higher speed in matching MMFs than thecurve 4 to 4' characteristic which represents a core fabricatedaccording to my 3,231,- 886 patent.

Referring now more particularly to FIG. 2, there is shown schematicallythree sets of core windings namely, a digital winding 10, an analogwinding 22 and a sense winding 28. It will be understood that allwindings 12, 22 and 28 are wrapped about a common annular transformercore in the same general manner as shown in my Pat. 3,231,886. In FIG. 2the reference character '17 indicates a precise current generated in thedigital circuit by a precise resistor in series to a precise voltage. Anunknown signal current is shown at 26 in the circuit for the analogwinding 22. These currents give rise to MMFs in both windings 10 and 22and these MMFs are caused to go towards zero when switches, indicated at19 in the digital circuitry and at 25 in the analog circuitry, move atthe same time to positions 20'and 24 respectively. While these switchesare shown as relay types, this is only for illustrative purposes and inpractice, the switches would be a pair of transistors.

In operation the digital MMF is changed by switching the current bymeans of a switch 16 to a different tap on the winding 10. Thus, forexample, a net MMF, such as indicated by vector 9 in FIG. 1, indicatingthat the analog signals exceed the digital signals, might mean that thedigital current transfers from tap 12 to tap 13 as shown in FIG. 2, thisbeing an increasing in MMF. It will be noted that the current remainsthe same, that is, there is only one precise resistor per decimaldigital (10 tap positions).

If the signal current 26 is not rerouted exactly at test time, then thesignal MMF, indicated by the vector 8 in FIG. 1 will stay constant asthe digital MMF, indicated by vector 7 in FIG. 1, goes toward zero.Then, if the signal exceeds the digits producing a net MMF, such asindicated at vector 9 in FIG. 1, then the resulting change of MMF fromvector 9 to vector 8 will not pass through the very narrow region 3 onthe curve of high permeability. That is to say, there will be verylittle flux change and kik voltage, thus the two opposing MMFs will becompared on the basis of kik voltage without rerouting the signalcurrent.

In very precise instruments, it is important that both switches 19 and25 operate within a fraction of a microsecond of one another. This istrue when there is an appreciable resistance, indicated at 29 in thesense circuitry, as then the kik can be large. That is, let the switch25 operate an instant before the switch 19, then in that instant, whichis the lag time of the switch 19, there will be a large MMF indicated bythe vector 7, which will cause an appreciable flux change due to thefalse large kik.

In FIG. 2 a switch 30 is shown as a short circuit across the sensewinding 28. Let the switches operate in the sequence indicated in FIG. 3which includes the lag time of the switch 19. In this case, a pulltowards a large steady state net MMF during this lag cannot appreciablyalter the condition of the true net MMF, since the short circuit doesnot allow voltage and therefore flux change. That is to say that the L/Rtime constant for a change of MMF is very much longer than the lag time.Then, subsequently, the opening of the switch 30, as shown in FIG. 3,permits the true kik which is then detected and used to alter thedigital MMF appropriately.

Having thus described the invention, what I claim and desire to obtainby Letters Patent of the United States is:

1. A magnetic digital ammeter, comprising:

(a) a core,

(b) said core being formed of magnetic material of small cross-sectionand characterized by initially high permeability,

(c) analog, digital and sense windings Wound about said core,

((1) first means for applying unknown signals to said analog windings toproduce a magnetic force in said core in one directio (e) second meansfor applying known digital signals to said digital winding to produce amagnetic force in said core in a direction opposite to the unknownforce,

(f) switching means connected to said analog and digital windings forcausing both of said forces to go to zero force and thus produce a backelectro-motive iforce having a net force in either of said directions,

(g) third means connected to said sense winding to detect the polarityof said net force,

(h) a series of taps connected to said digital windings,

(i) a switch connected to said second means and adapted to connect to aselected tap,

(j) said switch being responsive to said third means to position saidswitch with respect to said taps and thereby increase said digitalsignals until the known digital force balances the unknown analog force,

(k) switching means connected to said sense winding,

and

(l) timing means connected to said switching means for first actuatingthe switching means for said sense winding to short circuit said sensewinding then actuating the switching means for said analog and digitalwindings to cause said forces to go to zero force in close timedrelation to produce a back electro-motive force of a certain polaritywhereby the lag time between the analog and digital switching means willnot appreciably alter the operating point of said core, said senseswitching means then opening to sense a pulse of a polarity of theoriginal net force. I

2. A magnetic digital ammeter, comprising:

(a) a core of magnetic material having a hysteresis curve characterizedby a narrow region of high-permeability in the center of said curve andlow permeability elsewhere on said curve,

(b) analog, digital and sense windings disposed about said core,

(c) means for applying through said analog and digital windings opposingmagnetizing forces to said core,

(d) said sense winding adapted to detect the polarity of the net forcein said core,

(e) a series of taps connected to said digital winding,

(f) a precise current source,

(g) a switch connected to said source and adapted to connect to aselected tap,

(h) said switch being responsive to the output of said sense winding toposition said precise current with respect to said taps,

(i) switching means connected to each of said analog,

digital and sense windings, and,

(j) timing means connected to said switching means for first actuatingthe switching means for said sense winding to short circuit said sensewinding then actuating the switching means for said analog and digitalwindings to cause said forces to go to zero force in close timedrelation to produce a back electro motive force of a certain polaritywhereby the lag time between the analog and digital switching means willnot appreciably alter the operating point of said core, said senseswitching means then opening to sense a pulse of a polarity of theoriginal net force.

3. A magnetic digital ammeter comprising:

(a) a core of magnetic material having a high initial permeability,

(b) analog, digital and sense windings disposed about said core,

(0) means connected to said analog and digital windings for applyingopposing magnetic forces to said core,

(d) a switch provided for each of said windings and operativelyconnected to one another for operation in timed sequence,

(e) timing means connected to said switches for first References Citedactuating the switch for said sense winding to short UNITED STATESPATENTS circuit said sense Winding then actuating said analog anddigital switches to cause said opposing forces to 3,079,598 2/1963 Walt}340 347 go to zero force in close timed relation to produce 5 3,231,8861/1966 Slavln a back electro-motive force of a certain polarity wherebythe lag time between said analog and digi- MAYNARD WILBUR PrimaryExaminer tal switches will not appreciably alter the operating I.GLASSMAN, Assistant Examiner point of said core, said sense switch thenopening to sense a pulse of a polarity of the original net 10 C X-R-

